A Further Study on Large Size LSO and LYSO Crystal Samples

Transcription

1 October 25, 2005 IEEE NSS, N12-6, Puerto-Rico 1 A Further Study on Large Size LSO and LYSO Crystal Samples Jianming Chen, Liyuan Zhang, Ren-yuan Zhu California Institute of Technology

2 BGO, LSO & LYSO Samples % Ce in LSO/LYSO, 5--10% yttrium fraction in LYSO Cube: 1.7 cm (1.5 X 0 ), Bar: 2.5 x 2.5 x 20 cm (18 X 0 ) SIC BGO CPI LYSO Saint-Gobain LYSO CTI LSO 2

3 Experiment Without any thermal treatment, all samples went through measurement for optical and scintillation properties. Optical properties measured: transmittance, emission and excitation spectra. Light output and light response uniformity were measured with PMT and Si APD readout. Radiation induced phosphorescence intensity was measured for two LYSO long samples under γ ray irradiation, which was used to estimate readout noise with 100 ns gate. 3

4 Excitation, Emission & Transmittance Identical transmittance, emission & excitation spectra Part of emitted light is self-absorbed in long samples 1.7 cm Cube 2.5 x 2.5 x 20 cm Bar 4

5 CTI LSO: longitudinal optical uniformity No longitudinal variation in optical properties Transverse transmittance approaches theoretical limit 5

6 Emission Weighted Q.E. Areas under emission spectra proportional to the LY 59%/75% QE for LSO/LYSO readout with Si PD/APD 6

7 PMT Based Readout with Coincidence Systematic error with repeated mounts & measurements: < 1% 7

8 137 Cs & 22 Na Pulse Height Spectra Cube and bar samples have 8% and 10% FWHM resolution respectively for 137 Cs (0.66 MeV) and 22 Na source (0.51 MeV) CPI LYSO bar has double peak because of poor annealing Cube Bar 8

9 Light Output & Decay Time LSO/LYSO Light yield: a factor of 4/100 of BGO/PWO LSO/LYSO decay time: 42 ns compared to 300 ns of BGO Cube Bar 9

10 APD Based Readout with Coincidence Two Hamamatsu S APD, Canberra 2003 BT preamplifier and ORTEC 673 shaping amplifier with shaping time 250 ns Hamamatsu S APD 10

11 APD Readout Calibration Readout noise: 67 electrons for 2 APD with 250 ns shaping Systematic error with repeated mountings & measurements: 2.4% Calibration with Fe-55 source: 2.38 electrons/adc Channel 11

12 Pulse Height & Light Yield with APDs Na-22 annihilation peak (510 kev) well measured CTI LSO sample has significantly higher LO 12

13 LSO Light Response Uniformity Uniformity depends on end coupled to the PMT/APD, indicating a not uniform light yield along crystal 13

14 LYSO LRU Measured with APD Uniformity depends on which end coupled to the APD, indicating a not uniform light yield along crystal 14

15 γ ray Induced Readout Noise Sample L.Y. F Q 15 rad/h Q 500 rad/h σ 15 rad/h σ 500 rad/h ID p.e./mev μa/rad/h p.e. p.e. MeV MeV CPI 1, x x SG 1, x x γ ray induced PMT anode current can be converted to the photoelectron numbers (Q) integrated in 100 ns gate. Its statistical fluctuation contributes to the readout noise (σ). 15

16 CMS PWO Resolution 77k PWO Designed Resolution Energy Resolution: σ(e)/e < 1% if E > 25 GeV σ(e)/e ~ 0.5% at 120 GeV 2004 SM Beam Test Monitoring: 0.04% 16

17 LSO/LYSO ECAL Performance Less demanding to the environment because of small temperature coefficient. Radiation damage is less an issue as compared to the CMS PWO ECAL. A better energy resolution, σ(e)/e, at low energies than L3 BGO and CMS PWO because of its high light output and low readout noise: % / E 0.55% /E / E 17

18 Summary Ce doped LSO & LYSO crystals have fast (42 ns) and high (4 X BGO) light output. The light output of 2.5 x 2.5 x 20 cm LSO and LYSO samples, excited by 0.51 MeV γ ray, can be readout by Hamamatsu S APD (2 x 0.25 cm 2 ) with electronic noise of 70 electrons (< 35 kev). Longitudinal light response uniformity of long LSO/LYSO samples seems affected by Ce distribution along crystal. The radiation induced phosphorescence in 2.5 x 2.5 x 20 cm LYSO causes ~0.2 MeV 15 rad/h. An LSO/LYSO crystal calorimeter would provide very good energy resolution down to MeV range for future HEP experiments. To be understood: why LSO long sample has higher LO as compared to long LYSO samples with APD readout. 18

19 Possible Origin of Non Uniformity C. Melcher: LO in LSO is a function of Ce concentration B. Chai: LO in LYSO is a function of atomic fraction of Yttrium 19